In mammals, primordial germ cells cultured from the genital ridge have the ability to give rise to pluripotent embryonic stem cells. For example, U.S. Pat. Nos. 5,690,926 issued Nov. 25, 1997 to Hogan; 5,670,372 issued Sep. 23, 1997 to Hogan; and 5,537,357 issued Sep. 26, 1995 to Hogan each disclose pluripotential mammalian embryonic stem cells and methods of making the same. The disclosure of these patents is limited to mammalian embryonic stem cells and particularly to the culturing of murine and other mammalian embryonic stem cells using a combination of growth factors consisting of SCF, FGF and LIF.
Current prior art reports on the culture of avian primordial germ cells (PGCs) have concentrated on efforts to maintain a PGC-phenotype and to stimulate proliferation. See e.g., Chang, I. K. et al., Cell. Biol. Int. 1997 August; 21(8): 495-9; Chang, I. K. et al., Cell. Biol. Int. 1995 February; 19(2): 143-9; Allioli, N. et al., Dev. Biol. 1994 September; 165(1): 30-7 and PCT Publication No. WO 99/06533, published Feb. 11, 1999 (Applicant--University of Massachusetts; Inventors--Ponce de Leon et al.).
Undifferentiated avian cells expressing an embryonic stem cell (ESC) phenotype and processes for producing the same are disclosed in U.S. Pat. Nos. 5,340,740 issued Aug. 23, 1994 to Petitte et al.; 5,656,479 issued Aug. 12, 1997 to Petitte et al.; and 5,830,510 issued Nov. 3, 1998 to Petitte et al. Undifferentiated avian cells expressing an ESC phenotype are useful, among other things, as a tool for the study of embryological development (i.e., by labeling the cells with a marker gene and observing their distribution after injection in vivo) and the production of transgenic poultry. They are useful in allowing the application of homologous recombination to the production of transgenic poultry. In view of such uses, the development of additional methods for obtaining undifferentiated avian cells expressing an ESC phenotype represents a continuing need in the art.